Method for improving the cetane value of a hydrocarbon fuel oil



Patented Jan. 8, 1946 UNITED STATES PATENT OFFICE METHOD FOR HVIPROVING THE CETANE VALUE OF A HYDROCARBON FUEL OIL Henry G. Berger and Darwin E. Badertscher, Woodbury, N. .L, assignors to Socony-Vacuum Oil Company, Incorporated, a corporation of New York No Drawing. Application April 22, 194:.

' Serial No. 484,036

2 Claims. (01. 196-39) instant oi injection and the instant of ignition should be short. Improperly delayed ignition gives rise to the phenomenon known as knocking due to improper coordination of combustion and cylinder characteristics. By accelerating ignition of Diesel fuel it is possible to lower the compression pressure at which spontaneous ignition will occur without combustion shock, thereby increasing the ease of starting and smoothness with which combustion takes place.

As is well known to those familiar with the art, various additive compounds have been credited with the capacity to improve the ignition quality of Diesel fuels. Small amounts of such compounds incorporated in the fuel act as ignition accelerators. Another approach made to the problem presented by the relatively poor ignition quality of certain Diesel fuel is that which involves removing certain undesirable constituents from such fuels. Apparently, some of the constituents normally present in Diesel fuel prolong the ignition delay period; and in this way materially detract from the value of the fuel. In general, the removal of such constituents have been affected by physical methods, such, for example, as solvent extraction. The present invention is directed toward this problem but in contrast to extraction methods involves a chemical method for the removal of said constituents, rather than a physical method.

v The method contemplated herein is particularly valuable in view of the substantial improvement of the ignition characteristics of the fuel, and the value of the by-products obtained therewith. This method comprises treating a liquid hydrocarbon fuel with an aldehyde and an acid condensing agent thereby converting the undesirable constituents of the fuel to resinous materials, and then separating from the unreacted fuel the resinous materials so formed. Although the chemical mechanism involved in this method is not completely understood, these resinous materials presumably are formed by the action of the aldehyde and condensing agent upon the more aromatic'constituents of the fuel.

The present invention also contemplates an improved Diesel fuel obtained by the'method herein disclosed.

As contemplated herein, Diesel fuel is improved by treatment with aldehydes, either aliphatic,

aromatic or heterocyclic, in the presence of suitable acid condensing agents. Typical aldehydes useful for the purpose of this invention are formaldehyde, acetaldehyde, benzaldehyde, furfuraldehyde, etc. Formaldehyde is particularly preferred of such aldehydes in view of its availability, cost, and high degree of effectiveness in the present method. Representative of the numerous acid condensing agents which may be used in the present method are boron trifiuoride and the acids hydrofluoric, hydrochlori and sulfuric; of these condensing agents, hydrofluoric acid is preerred.

The method contemplated herein, for the reone of the many ways known in the petroleumand chemical arts for treating hydrocarbon fractions. For example, all three components-fuel, aldehyde and condensing agent-may b mixed and agitated under suitable conditions, or the same components may flow together through a suitable reaction vessel. Also, two of these components may flow countercurrently to the third component in such a vessel. It will be apparent to those familiar with the art that these three components may be so contacted in the presence of an absorptive material, such as an absorptive clay. In such case the resinous materials are adsorbed on the clay as fast as they are formed. While hydrofluoric acid may be used in aqueous solution, it is preferred to use the anhydrous form. Formaldehyde, for example, may be used either in the gaseous phase or solid phase, depending upon the temperature involved; and may even be used in aqueous solution. Elevated temperatures up to the cracking temperature of the fuel may be used herein, however, satisfactory results are obtained with temperatures from about 10 C. to about C., and to about 200 0. As will be seen hereinafter, temperatures of the order of 20 C. to 25 C. are particularly convenient and desirable. Although atmospheric pressure serves the purposes of this invention, it is preferred to use elevated pressure, for with the latter a greater degree of contact of the three components'is overnight at room temperature.

realized. After a suitable length of time, which may vary from several seconds to several hours, depending upon the manner in which the three components are brought together and depending upon the quantities of the same, the resinous material so formed is separated from the reaction mixture. For example, the reaction mixture may be distilled, the distillate obtained therefrom will be the improved fuel and the residue will be the resinous material into which the undesirable constituents of the fuel were converted. Other means, however, may be resorted to in order to separate the improved fuel and said resinous material. Some examples of such means are: solvent extraction, precipitation by dilution with various liquids (such as butane, petroleum ether,

etc.) at suitable temperatures, absorption on absorptiveclays and similar materials, etc.

The quantities of Diesel fuel, aldehyde and acid condensing agent used herein may be varied considerably, such quantities depending upon the degree of improvement to be attained, the extent of the undesirable constituents in the fuel, the various conditions used in the treatment, etc. For example, a low cetane number fuel, having a relatively high aromatic or cyclic content, would, in general, require a rather heavy treatment with an aldehyde and condensin agent to effect improvement. Similarly, a high cetane number fuel, having a comparatively low cyclic content, would generally require only a light treatment with a relatively small amount of'aldehyde and condensing agent to effect improvement. The quantities used in Example I below will serve as illustrations.

Example I will serve to illustrate the present method, and the improved fuel and resinous material obtained therewith. Example 11 is shown in order to demonstrate that improvement in the ignition quality of the "Base fuel," described below,'is not achieved through the use of relatively high temperature alone.

Example I v In this example, a typical low-grade Diesel fuel,

having the following properties and identified hereinafter as Base fuel," was used:

A. P. I. gravity.. 18.9 Aniline number 47.8 Pour point F-.. -35 Flash point (Pensky-Martens). F. 198 Carbon residue -e per cen 0.2 Sulfur content do 0.1

A. S. T. M. distillation:

Cetane number -s 23.5

The treatment was carried out in three batches, 600 cc. of Base fuel being treated in each batch. A mixture of 600 cc. of Base fuel," 90 to 128 grams of trioxymethylene (solid polymeric formaldehyde) and 35-40 cc. of anhydrous hydrofluoric acid were stirred in an open copper beaker for about three hours in an ice bath, and then After adding benzol to the reaction mixture, the resulting olution was filtered and then washed with water to remove unreacted acid and unreacted trioxymethylene. The washed benzol solution was again carefully filtered and then carefully fractionated to remove the benzol therefrom. Now, the three benzoi-free batches were combined and distilled to a final flask temperature of 300 C. at 150-200 mms. pressure. The distillate was the improved fuel, designated herein as .Fuel A. The residue was a relatively high melting, hard, rather brittle, red-green resin, weighing about 200 grams.

Example II Eight hundred (800) cc. of the Base fuel" was subjected to distillation to a final flask temprrature of 300 C. under 150-200 mms. pressure. The residue, 37.5 grams, was a black, non-resinous material. The distillate is referred to hereinafter as Fuel 13.

The effectivness of the method illustrated above in Example I, in improving the ignition quality of the "Base fuel," is demonstrated by comparative test results of the Base fuel" and of Fuel A." A similar test result of "Fuel B'Kdemonstrates the ineffectiveness of distillation, at relatively high temperature, as a means to improve the ignition quality of the Base fuel."

The ignition quality of each of the three fuels Base fuel, Fuel A," and Fuel B"-was determined by comparison with a standard reference fuel in a converted C. F. R, engine using the ignition delay method. The value obtained in this test is expressed as the cetane number" which is the per cent by volume of cetane and alpha-methyl naphthalene having the same combustion characteristics as the sample under test (reference: Proc. Amer. Soc. Testing Materials, vol. 36,1, 418 (1936)).

Test results obtained as outlined above are tabulated in the table below.

It will be seen from the foregoingresults that the method contemplated herein provides a means for improving the ignition quality of a typical Diesel fuel, thusproviding a more valu.

able fuel. It will also be seen that mere distillation (at relatively high temperature) of a typical Diesel fuel does not furnish a fuel having a better ignition quality, rather the fuel so obtained has a lower ignition quality.

It is to be understood that the term "Diesel fuel" as used herein is inclusive of all types of non-viscous hydrocarbon fuel oils intended for use in any compression ignition engine. It is to be further understood that the foregoing example (Example I) is illustrative only of the method contemplated herein, and that the invention is not limited to this one example, The present invention, therefore, embraces within its scope such changes and modifications as fairly come within the spirit of the, appended claims,

We claim:

1. The method for improving the cetane value of a hydrocarbon fuel oil containing aromatic constituents and characterized by a relatively low cetane value, which comprises: treating said fuel oil with substantiall only an aliphatic aide hyde and hydrofluoric acid, thereby converting said aromatic constituents to resinous materials:

2,392,570 3 from said aromatic constituents and characterand anhydrous hydrofluoric acid, thereby conized by a cetan'e value substantially greater than verting said aromatic constituents to resinous the cetane value of the untreated fuel oil, from materials; and separating said iuel oil substansaid resinous materia tially free from said aromatic constituents and 2. The method for improving the cetane value 5 characterized by a cetane value substantially of a hydrocarbon fue1 oil containing aromatic greater than the cetane value 0! the untreated constituents and characterized by a relatively fuel oil, irom said resinous materials. low cetane value, which comprises; treating said HENRY G. BERGER. fuel oil with substantially only trioxymethylene DARWIN E, BADERTSCHER. 

